Conventional energy using devices including internal-combustion engines for automobiles, boilers, heat exchangers used for air-conditioning equipment, power generators, electric mechanisms such as motors, and light-emitting devices such as illuminators release or lose much thermal energy as waste heat, light, or the like.
In recent years, from the viewpoint of energy saving, it has been required to collect the released thermal energy and reuse such energy as the energy source. As such a system, a power generation system has been suggested. Specifically, this power generation system includes, for example, a heat source of which temperature is increased or decreased over time, a first device, and a second device. The first device (such as a dielectric) is electrically polarized by the piezo effect, the pyroelectric effect, the Seebeck effect, or the like in accordance with the temperature change of the heat source. The second devices (such as electrodes) are disposed opposite to each other with the first device interposed therebetween in order to extract electric power from the first device. Moreover, mounting the power generation system in an automobile or the like and moreover, in such a case, having the first device (such as a dielectric) in an exhaust pipe to which the exhaust gas of the automobile is supplied have been suggested (see, for example, Patent Literature 1).
For more efficient power generation of such a power generation system, applying voltage to the first device in accordance with the temperature condition of the first device has been examined.
Specifically, for example, the temperature of the first device is detected by the temperature sensor (such as a thermocouple or a thermistor) and upon the detection of the temperature increase in the temperature sensor, the voltage is applied to the first device.
However, the responsiveness to the temperature change is different between the temperature sensor and the dielectric as the first device. Thus, when the voltage is applied to the first device on the basis of the temperature detected by the temperature sensor, the responsiveness of the applied voltage relative to the temperature detection is not sufficient. For the higher power generation efficiency, the higher responsiveness may be required.
In the power generation system, the higher power generation efficiency is attempted by stopping the voltage application at the timing when the temperature of the first device has decreased.
On the other hand, further higher power generation efficiency of the power generation system has been required.